Stability lithium polymer batteries

The lithium polymer battery (LPB), shown schematically in Fig. 7.21, is an all-solid-state system which in its most common form combines a lithium ion conducting polymer separator with two lithium-reversible electrodes. The key component of these LPBs is the polymer electrolyte and extensive work has been devoted to its development. A polymer electrolyte should have (1) a high ionic conductivity (2) a lithium ion transport number approaching unity (to avoid concentration polarization) (3) negligible electronic conductivity (4) high chemical and electrochemical stability with respect to the electrode materials (5) good mechanical stability (6) low cost and (7) a benign chemical composition. 

Molecular salts of type 65 have also been prepared recently by the reaction of a secondary amine with the linear isomer of hexafluoropropane sultone as depicted in Scheme 18 <2003MI1961>. These lithium polymers exhibit high electrochemical stability and cationic conductivity and therefore are ideally suited for lithium polymer batteries. 

The polymer component in these batteries fulfills the function of a medium for ionic transport and a separator. The polymers are polyethers, PEO, or PPO. However, the lithium salts, dissolved in these polymers, have 100-fold lower conductivity than that of a lithium salt dissolved in water. The low conductivity below 70 °C, the reactivity of the interface with the lithium metal electrode, and the issues related to mechanical properties and electrochemical stability need to be resolved before the lithium polymer battery has acceptable performance. The use of inorganic composite membranes, described in a subsequent section, has been shown to result in improved ionic conductivity. 

Ion conducting polymers may be preferable in these devices electrolytes because of their flexibility, moldability, easy fabrication and chemical stability (for the same reasons that they have been applied to lithium secondary batteries [19,48,49]). The gel electrolyte systems, which consist of a polymeric matrix, organic solvent (plasticizer) and supporting electrolyte, show high ionic conductivity about 10 5 S cnr1 at ambient temperature and have sufficient mechanical strength [5,7,50,51], Therefore, the gel electrolyte systems are superior to solid polymer electrolytes and organic solvent-based electrolytes as batteries and capacitor materials for ambient temperature operation. 

The strategy of hybrid and gel electrolytes is very promising for lithium-ion batteries, but it seems less viable for lithium-metal batteries due to the reactivity of lithium metal with the encapsulated solvent. In fact, high conductivity is not the only parameter in selecting a successful polymer electrolyte for the development of lithium batteries a low interface resistance and a high interface stability over time are also required to assure good cyclability and long life. 

The ceramic fillers (e.g., AI2O3, SiOa, TiOa) can greatly influence the characteristics and properties of polymer electrolyte by enhancing the mechanical stability and the conductivity [135, 175-178]. Prosini et al. [179] in a PVdF-HFP polymer matrix used y-LiAlOa, AI2O3, and MgO as fillers to form self-standing, intrinsically porous separators for lithium-ion batteries. The MgO-based separators showed the best anode and cathode compatibilities. 

Alternatively, a roll can be wound to fit a prismatic case as commonly found in lithium ion batteries. The roll is placed in a fitted conductive metal casing that has a Teflon or rubber gasket seal separating the outer can and top button contact. The cylindrical metal rod around which the film is wound becomes the internal contact. Contacts are ensured by soldering and then electrolyte is injected into the cell followed by a curable polymer sealant. The top of the casing is fitted with a vent, gasket layer, and top contact plate. To seal the device, the top of the can is mechanically crimped and the outer metal casing acts as the other contact and provides mechanical stability and rupture resistance. 

It is speculated that the polymerization mechanism in Eq. 4 involves two steps. Once 1,4-dimethoxybenzene is oxidized, a radical cation will be formed, and the radical cation can be further stabilized by losing a proton with no charge bearing on the aromatic ring (see Equation 5). The resulted radical can attack other 1,4-dimethoxybenzene molecule as shown in Equation 6. After the polymerization reaction, 1,4-dimethoxybenzene will be converted into a polymer and lose shuttle capability. Hence, 1,4-dimethoxybenzene cannot be a reversible redox shuttle for lithium-ion batteries. 

Shimonishi Y, Zhang T, Imanishi N, Im D, Lee D-J, Hirano A, Takdeda Y, Yamamoto O, Sammes N (2011) A study on hthium/air batteries-Stability of the NASICON-type lithium ion conducting sohd electrolyte in alkaline aqueous solutions. J Power Sources 196 5128 Imanishi N, Yamamoto O (2014) Polymer electrolyte for lithium-air batteries. In Scrosati B, Abraham KM, Schahcwijk W, Hassoun J (eds) Lithium batteries advanced technology and apphcations. Wiley and ECS, p 217... 

In particular, in lithium metal polymer batteries, dendritic growth of lithium on a lithium anode, formation of dead lithium, interfacial phenomenon between the lithium anode and the polymer electrolyte, etc., adversely affects the stability and cycle characteristics of the batteries. In view of these problems, various polymer electrolytes have been developed. 

Since both neutral and reduced forms of (CH) have good stability in a battery employing lithium perchlorate in tetrahydrofuran solvent, a cell was constructed using the above polymer electrodes. It is the first stable, fully polymer, rechargeable battery with Coulombic efficiencies greater than 99%. A cell of this type, using 7% doped anode, has an open-circuit potential of 1 V and current of approximately 30 Am of (CH). ... 

---